Scientific Name:Didemnum vexillum
Common Name:Didemnum tunicate (others: colonial sea squirt, carpet tunicate)
Established Range:On the East Coast, from Maritime Canada to Maryland
Established in Rhode Island?Yes, throughout Narragansett Bay
Date and Location of Introduction:1970, New England
Method of Introduction:Unknown, but likely through hull fouling, or with contaminated shellfish stock
Habitat:Individual zooids of D. vexillum grow together in large groups called colonies. Colonies can be found in the subtidal zone, attached to rocks, boulders, and artifical structures such as pilings and floating docks. D. vexillum can also be found growing over seaweeds, sponges, shellfish, and other tunicates. D. vexillum can grow at depths up to 65 meters, and can tolerate temperates from -2 to 24° Celsius.
Average Life Span:Unknown
Diet:D. vexillumis a filter feeder that eats zooplankton, phytoplankton, and detritus.
Breeding:D. vexillumis hermaphroditic and breeds sexually by broadcast spawning and asexually by budding.
Concerns:All invasive tunicates, including D. vexillum, pose the same problems. These tunicates are notorious fouling organisms, and can completely cover submerged boat hulls, aquaculture cages, and just about any other surface that they are capable of living on. As a result, they can slow down boats and have negative impacts on the local environment. Invasive tunicates have been known to smother shellfish and other sessile organisms, and will outcompete native filter feeders for food and space.
Control:D. vexillum can be removed from an infested object by scraping them off and placing them in the garbage or letting them dry out. If you choose to pressure wash colonial tunicates off equipment, only do so on land and make sure the resulting wastewater does not go back into the sea, as these tunicates can often re-grow from small fragments. Additionally, D. vexillum can be removed from shellfish with acetic acid and bleach treatments. Wrapping affected areas in plastic has also been tried as a control method, with some success.
Identification Card:Courtesy of Salem Sound Coastwatch
- WASHINGTON STATE’S RESPONSE TO AN INVASION OF NON-NATIVE TUNICATES
- Treatment methods used to manage Didemnum vexillum in New Zealand (PDF)
- Development of a method to reduce the spread of the ascidian Didemnum vexillum with aquaculture transfers
- An evaluation of incursion response tools for invasive species: a case study of Didemnum vexillum in the Marlborough Sounds
Works Cited:Cohen, Andrew N. 2005 Guide to the Exotic Species of San Francisco Bay. San Francisco Estuary Institute, Oakland, CA, www.exoticsguide.org
Denny, C.M. 2008. Development of a method to reduce the spread of the ascidian Didemnum vexillum with aquaculture transfers. ICES Journal of Marine Science Advance Access, p. 1-6
ISSG. 2007. Ecology of Didemnum sp. The Global Invasive Species Database, http://www.issg.org/database